Solve for $x$ and $y$ using elimination. ${-5x-y = -21}$ ${-4x-y = -18}$
Explanation: We can eliminate $y$ by adding the equations together when the $y$ coefficients have opposite signs. Multiply the bottom equation by $-1$ ${-5x-y = -21}$ $4x+y = 18$ Add the top and bottom equations together. $-x = -3$ $\dfrac{-x}{{-1}} = \dfrac{-3}{{-1}}$ ${x = 3}$ Now that you know ${x = 3}$ , plug it back into $\thinspace {-5x-y = -21}\thinspace$ to find $y$ ${-5}{(3)}{ - y = -21}$ $-15-y = -21$ $-15{+15} - y = -21{+15}$ $-y = -6$ $\dfrac{-y}{{-1}} = \dfrac{-6}{{-1}}$ ${y = 6}$ You can also plug ${x = 3}$ into $\thinspace {-4x-y = -18}\thinspace$ and get the same answer for $y$ : ${-4}{(3)}{ - y = -18}$ ${y = 6}$